Re: [PATCH [repost]] block/blkio: Don't assume size_t is 64 bit

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Tue, Jan 30, 2024 at 12:19:37PM +0000, Richard W.M. Jones wrote:
> On Tue, Jan 30, 2024 at 01:04:46PM +0100, Kevin Wolf wrote:
> > Am 30.01.2024 um 11:30 hat Richard W.M. Jones geschrieben:
> > > On Tue, Jan 30, 2024 at 09:51:59AM +0100, Kevin Wolf wrote:
> > > > Am 29.01.2024 um 19:53 hat Richard W.M. Jones geschrieben:
> > > > > With GCC 14 the code failed to compile on i686 (and was wrong for any
> > > > > version of GCC):
> > > > > 
> > > > > ../block/blkio.c: In function ‘blkio_file_open’:
> > > > > ../block/blkio.c:857:28: error: passing argument 3 of ‘blkio_get_uint64’ from incompatible pointer type [-Wincompatible-pointer-types]
> > > > >   857 |                            &s->mem_region_alignment);
> > > > >       |                            ^~~~~~~~~~~~~~~~~~~~~~~~
> > > > >       |                            |
> > > > >       |                            size_t * {aka unsigned int *}
> > > > > In file included from ../block/blkio.c:12:
> > > > > /usr/include/blkio.h:49:67: note: expected ‘uint64_t *’ {aka ‘long long unsigned int *’} but argument is of type ‘size_t *’ {aka ‘unsigned int *’}
> > > > >    49 | int blkio_get_uint64(struct blkio *b, const char *name, uint64_t *value);
> > > > >       |                                                         ~~~~~~~~~~^~~~~
> > > > > 
> > > > > Signed-off-by: Richard W.M. Jones <rjones@redhat.com>
> > > > 
> > > > Why not simply make BDRVBlkioState.mem_region_alignment a uint64_t
> > > > instead of keeping it size_t and doing an additional conversion with
> > > > a check that requires an #if (probably to avoid a warning on 64 bit
> > > > hosts because the condition is never true)?
> > > 
> > > The smaller change (attached) does work on i686, but this worries me a
> > > little (although it doesn't give any error or warning):
> > > 
> > >     if (((uintptr_t)host | size) % s->mem_region_alignment) {
> > >     error_setg(errp, "unaligned buf %p with size %zu", host, size);
> > >         return BMRR_FAIL;
> > >     }
> > 
> > I don't see the problem? The calculation will now be done in 64 bits
> > even on a 32 bit host, but that seems fine to me. Is there a trap I'm
> > missing?
> 
> I guess not.  Stefan, any comments on whether we need to worry about
> huge mem-region-alignment?  I'll post the updated patch as a new
> message in a second.

An alignment of 32 or more bits is not required in any scenario that I'm
aware of.

Stefan

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